One approach to the utilization of polymer-bound rubber chemicals is to prepare a masterbatch rubber and then blend down to the desired level with the rubber in which the chemical is intended to function. In the case of rubbers prepared in aqueous emulsions or already existing in a latex form, the blending is preferably done at the latex stage. The blending may also be conducted in the dry rubber state using conventional mixing techniques common to the rubber industry.
There exists the need to prepare polymers with high levels of polymer-bound rubber chemicals. One route to such highly loaded polymers entails the use of copolymerizable functionalized monomers. Many copolymerizable monomers having rubber chemical functionality are polar, high melting solids which are only slightly soluble in the monomers typically employed to prepare rubbers, i.e. butadiene, isoprene, styrene or acrylonitrile. The solubility of these chemicals limits the level to which they can be copolymerized and thus the extent to which they may be utilized in the masterbatch blending technique.
U.S. Pat. Nos. 3,658,769, 3,767,628 and 4,213,892 describe the preparation of compounds such as N-(4-anilinophenyl)methacrylamide and N-(4-anilinophenyl)acrylamide and the polymerization of such compounds with typical monomers. It is apparent from these patents that the copolymerizable antioxidants could only be incorporated into the polymers at relatively modest levels which, although sufficient to confer good age resistance or oxidation protection to the rubbers, are not high enough for practical use in masterbatch blending techniques. These references disclose that a solvent such as methyl ethyl ketone or isopropyl alcohol may be required to obtain adequate solubility of the monomers as well as to solubilize other ingredients where required. The references do not suggest that the use of MIBK in conjunction with elevated soap levels would provide for unexpectedly high levels of incorporation of functionalized monomers in emulsion polymerizations.
U.S. Pat. No. 4,521,574 discloses the use of dichloromethane (DCM) and/or tetrahydrofuran (THF) as cosolvents in an emulsion polymerization; however, DCM and THF have been determined to be a potential environmental and health concern.
The prior art has suggested the use of methyl ethyl ketone as a cosolvent to promote the incorporation of functionalized monomers; however, due to methyl ethyl ketones solubility in water, it was determined that use of methyl ethyl ketone resulted in a two phase system that is highly undesirable. It has been discovered that the use of MIBK does not result in a two phase system and thus forms a portion of the instant invention.